The following documents are considered to be relevant for an understanding of the background of the invention:
Barkana, Y and Belkin M., Selective Laser Trabeculoplasty, Survey of Ophthalmology 52:634-653, 2007.
U.S. Pat. No. 6,698,886 to Pollack et al.
U.S. Pat. No. 5,479,222 to Volk.
Under normal circumstances, aqueous humor is secreted the posterior chamber of the eye, and then circulates through the pupil into the anterior chamber where it passes through the trabecular meshwork, before being secreted from the eye. In most forms of glaucoma, the flow of the aqueous humor through the trabecular meshwork is impeded, preventing adequate drainage of the aqueous humor from the eye. This leads to a rise in the intraocular pressure, a state which may cause damage to the eye and lead to progressive blindness. One method to treat or prevent this from occurring is to alter some of the trabecular meshwork in order to improve the flow of aqueous humor through the trabecular meshwork.
A common method of enhancing the flow of aqueous humor through the trabecular meshwork is laser trabeculoplasty (LTP) which consists of the application of laser energy to the trabecular meshwork. There are a several types of LTP, such as selective laser trabeculoplasty (SLT) argon laser trabeculoplasty (ALT), diode laser trabeculoplasty (DLT), micropulse laser trabeculoplasty (MLT), and titanium: sapphire laser trabeculoplasty (TLT). The various types of LTP differ in the wavelength and other characteristics of the laser beam. SLT, for example, utilizes a Q-switched 532 Nd:YAG laser which selectively targets melanin-containing cells within the trabecular meshwork. (Barkana, Y et al) While the entire mechanism of action has not been completely elucidated, it is believed that laser-stimulated melanin-containing cells release cytokines which attract other cell types to the trabecular meshwork that increase its permeability. Unlike older versions of LTP, such as ALT, selective laser trabeculoplasty does not require precise targeting since the wavelength and energy of the light used selectively targets the melanine containing cells within the meshwork. The surrounding cells are not heated or destroyed. Thus, the fluid outflow is improved without damaging the trabecular meshwork. SLT has been used to treat primary open angle glaucoma, intraocular hypertension, normal tension glaucoma, aphakic (glaucoma in patients without a natural lens in their eye), pseudophakic glaucoma (glaucoma in patients without an artificial lens in their eye pigmentary, chronic angle closure glaucoma and juvenile glaucoma. SLT has also been successfully used to treat pressure increases in the eye caused by certain medications.
FIG. 1 shows the treatment of an eye 1 by LTP. Eye drops are first placed in the eye to provide surface anesthesia and to prepare the eye for the procedure. The trabecular meshwork 10 is situated around the angle of the anterior chamber of the eye and is not directly observable because it is obscured by the limbal area 12. A gonioscopic contact lens 2 which includes a mirror 3 is applied to the eye 1 to direct a laser beam 6 through the cornea S to the trabecular meshwork 10 underneath the limbal area 12. Typically, between 180° to 360° of the anterior chamber angle is irradiated by rotating the gonioscopic contact lens 12 after each laser pulse. About 100 laser pulses of a few nanoseconds duration and about 0.6 to 200 mJ of energy are delivered to the trabecular meshwork.
U.S. Pat. No. 5,479,222 to Volk discloses a gonioscopic lens system comprising at least two lenses. At least one of the lenses includes an aspheric surface of revolution. The lenses are positioned adjacent one another in a housing, such that the refractive properties of each are combined to converge light from an illumination light source to the entrance pupil of the patient's eye to illuminate the fundus. The lens system is designed for use with an associated ophthalmoscopic lens, enabling selective modification of the optical characteristics of the ophthalmoscopic lens system in a predetermined manner.
U.S. Pat. No. 6,698,886 to Pollack et al discloses an iridotomy and trabeculoplasty goniolaser lens having a contact lens element, a planar mirror offset from the optical axis of the contact lens element and first and second button lenses mounted on the anterior surface of the contact lens element. Magnification, curvature and location of the button lenses are chosen so as to provide the ability to simultaneously deliver laser energy to the iris of a patient's eye along a first optical path offset from the optical axis of the contact lens element and to view the trabecular meshwork around the region where the laser energy was applied.
Irradiating the trabecular meshwork with a laser beam directed through the cornea, as shown in FIG. 1, is often not possible in cases of narrow or closed angle glaucoma which occurs when the iris of the eye approaches the cornea and thus narrows or eliminates the angle between the cornea and the iris. This is the most common type of glaucoma in Chinese and Indian people and hence the commonest form of glaucoma and blindness in the world. In these cases, the laser beam cannot reach the trabeculum meshwork to be irradiated.